1. Field of the Invention
The present invention relates to an epitaxial wafer for laser diodes, preferably suitable for AlGaInP-based red laser diodes, and a method for producing the epitaxial wafer.
2. Description of the Related Art
Red laser diodes (LDs) using AlGaInP-based semiconductors are widely used as a light source for DVD read/write.
FIG. 3 shows a cross-sectional schematic structure of a conventional AlGaInP-based LD epitaxial wafer.
As shown in FIG. 3, the epitaxial wafer is formed by using metal organic vapor phase epitaxy (MOVPE), sequentially stacking, on an n-type GaAs substrate 11, an n-type AlGaInP cladding layer 12, an undoped active layer 13, a p-type AlGaInP cladding layer 14 and a p-type cap layer 15.
During the p-type AlGaInP cladding layer 14 growth, diethylzinc (DEZ), dimethylzinc (DMZ) or the like is supplied as a doping raw material to cause zinc (Zn) (=p-type carrier) to be contained in the p-type AlGaInP cladding layer 14, to form the p-type AlGaInP cladding layer 14 (See, e.g., JP-A-2002-25920).
As mentioned above, in the conventional LD epitaxial wafer, the p-type AlGaInP cladding layer is caused to contain zinc (Zn) as its p-type carrier, but Zn is highly diffusive, and therefore diffuses into its adjacent layer. The Zn diffusion causes the problems of (1) non-uniform carrier concentration (═Zn concentration) in the depth direction of the p-type cladding layer, and (2) Zn invasion into the adjacent active layer. The device processing of the epitaxial wafer having the problems of (1) and (2) causes deterioration in laser diode properties, such as an increase in operation current Iop that is an important device property. Thus, the increase in operation current Iop will lead to a serious problem of being low in laser diode reliability, i.e., in its lifetime.